Problems after installing a new XFX HD4850

After getting a new XDX HD4850, and fitting it with no problems whatsoever, my computer seems to be alot slower than it used to be, i.e.: taking longer to load things etc. My computer also crashes alot and just restarts instantly and then when it starts up says that the system has recovered from a serious error.

I have ruled out the following problems that could cause these types of issues:
-Overheating
-GFX card not compatible; the graphics card works wonders for gaming and can max out CoD4 and Crysis with 0 problems.

The only thing I can think that is wrong is the main hard drive, ever since I fitted the new graphics card, I had to move the SATA cable from Chan1 to Chan4 because the GFX card physically took up too much room on my motherboard. Ever since this, it takes 30 seconds to copy 40mb of data, which used to be instant, also, when playing COD4 or other games sucgh as crysis, sometimes it can take 3 minutes to load a map, when other times it takes about 10 seconds..

Any help is much appreciated, this has become ridicules and is starting to really bug me!

Do you happen to have the HDMI port and Windows XP? I remember reading that XP does not support the audio chip correctly and it causes a massive amount of interrupts, thus slowing your machine down since it's servicing hardware interrupts like crazy.

Check under Device Manager and see if there is a 2nd audio card...if so, disable it and reboot.